The present invention relates to the construction of a brushless motor for use in a disc-driving apparatus or the like employed mainly in an information processing field.
In recent years, there have been increasing developments of disc-driving apparatuses which are compact and of high density. FIGS. 13 and 14 show a representative example of a product in the field relating to the present invention. The product shown in FIGS. 13 and 14 is a 2.5-inch magnetic disc-driving apparatus developed by PrairieTek Corp. of the U.S.A. The drawings of FIGS. 13 and 14 are copied from a catalog of the product. There are demands for the development of portable type apparatuses having high quality, namely, apparatuses which are compact, resistant to shock, make little noise, vibrate little, and consume a small amount of electricity. Needless to say, there are also demands for the development of a high quality brushless motor (abbreviated as "motor" in descriptions made below) for rotating a disc. Manufacturers are conducting research to comply with the above demands. Further, it is necessary for manufacturers to improve productivity not only in producing motors but also in assembling apparatuses.
A bearing is one of the elements which determines the performance of the motor. As in the apparatus shown in FIGS. 13 and 14, a ball bearing has been conventionally used as the bearing. A dynamic pressure fluid bearing has drawn attention and has been adopted as a bearing which complies with the demands at a high level. The dynamic pressure fluid bearing comprises a cylindrical shaft; a hollow cylindrical metal sleeve fitted thereon with a gap provided therebetween; and a herringbone groove provided on the shaft or the sleeve. Lubricating fluid (oil) is filled in the gap. With the rotation of a rotor, pressure is generated in the fluid, thus supporting the rotor. Theoretically, the dynamic pressure fluid bearing is superior as the bearing of the apparatus according to the present invention, because the mechanism thereof has a small volume; makes little noise because the rotor is supported through oil; is resistant to shock; is not subject to the shaft becoming significantly eccentric due to intergration effect because the load is received by the entire periphery of the shaft. The dynamic pressure fluid bearing has, however, a disadvantage that the performance thereof deteriorates when oil becomes scanty and that an apparatus is polluted by oil which flows out therefrom. Thus, it is necessary to solve this problem.
In addition to solving the problem of the dynamic pressure fluid bearing having a smaller volume and making less noise than the ball bearing, improvements are desired for other constituent elements of the motor. More specifically, there are demands in particular for an improvement in the winding density of a coil and a reduction in the vibration of a bracket and the like.
There is also a demand for an improvement in the construction of a portion for electrically connecting a member of the motor of a disc-driving apparatus and a control circuit thereof with each other. Conventionally, a terminal wire (called a lead wire in the followings description of a driving coil is manually connected with a printed wiring board by soldering. But recently, it has become very difficult to perform this operation due to the miniaturization of the motor, and hence the development of a novel connection method is desired. Conventionally, a flexible substrate and a connector are used to connect the coil and the control circuit, which makes it difficult to automate the connection between the connector and the control circuit. The miniaturization of the motor and the apparatus causes another problem in that the volume of the flexible substrate and that of the connector are great relative to the volume of the motor and that of the apparatus.
Further, a hole used to insert the flexible substrate into the motor and remove it therefrom is sealed with sealing agent consisting of adhesive agent to prevent air from permeating thereinto. Thus, skilled work and much time are required to seal the hole.
In addition, it is important to prevent the quality of the motor from being deteriorated in the process of assembling the motor. The motor constituting the disc-driving apparatus is composed of precision parts, for example, the bracket, but the precision of the parts may be degraded when handled in the assembling operation. The bracket constitutes the base of the motor, thus frequently contacting a motor-placing platform. Therefore, there is a possibility that the finished surface of the bracket will be damaged or soiled. Thus, before a product is shipped, whether or not the finished surface of the bracket has been damaged or soiled is checked with a microscope. In this situation, the development of damage-preventing countermeasures is desired.